﻿Double 
  Adaptations 
  451 
  

  

  stems, 
  a 
  dense 
  foliage, 
  a 
  strongly 
  cuticularized 
  

   epidermis, 
  few 
  and 
  narrow 
  air-cavities 
  in 
  the 
  

   tissues 
  and 
  all 
  the 
  long 
  range 
  of 
  characteris- 
  

   tics 
  of 
  typical 
  desert-plants 
  are 
  not 
  a 
  simple 
  

   result 
  of 
  the 
  influence 
  of 
  climate 
  and 
  soil. 
  

   There 
  is 
  no 
  direct 
  influence 
  in 
  this 
  sense. 
  

  

  The 
  second 
  point, 
  in 
  which 
  Nageli's 
  idea 
  is 
  

   broken 
  down 
  by 
  Holtermann's 
  observations, 
  re- 
  

   sults 
  from 
  the 
  behavior 
  of 
  the 
  plants 
  of 
  the 
  

   Kaits 
  desert 
  when 
  grown 
  or 
  sown 
  on 
  garden- 
  

   soil. 
  When 
  treated 
  in 
  this 
  way 
  they 
  at 
  once 
  

   lose 
  the 
  only 
  peculiarity 
  which 
  might 
  be 
  con- 
  

   sidered 
  as 
  a 
  consequence 
  of 
  the 
  desert-life 
  of 
  

   their 
  ancestors, 
  their 
  dwarf 
  stature. 
  They 
  be- 
  

   have 
  exactly 
  like 
  the 
  alpine 
  plants 
  in 
  Bonnier 
  *s 
  

   experiments, 
  and 
  with 
  even 
  more 
  striking 
  dif- 
  

   ferences. 
  In 
  the 
  desert 
  they 
  attain 
  a 
  height 
  

   of 
  a 
  few 
  centimeters, 
  but 
  in 
  the 
  garden 
  they 
  

   attain 
  half 
  a 
  meter 
  and 
  more 
  in 
  height. 
  Noth- 
  

   ing 
  in 
  the 
  way 
  of 
  stability 
  has 
  resulted 
  from 
  the 
  

   action 
  of 
  the 
  dry 
  soil, 
  not 
  even 
  in 
  such 
  a 
  minor 
  

   point 
  as 
  the 
  height 
  of 
  the 
  stems. 
  

  

  From 
  these 
  facts 
  and 
  discussions 
  we 
  may 
  

   conclude 
  that 
  double 
  adaptation 
  is 
  not 
  induced 
  

   by 
  external 
  influences, 
  at 
  least 
  not 
  in 
  any 
  way 
  

   in 
  which 
  it 
  might 
  be 
  of 
  use 
  to 
  the 
  plant. 
  It 
  

   may 
  arise 
  by 
  some 
  unknown 
  cause, 
  or 
  may 
  

   not 
  be 
  incited 
  at 
  all. 
  In 
  the 
  first 
  case 
  the 
  plant 
  

   becomes 
  capable 
  of 
  living 
  under 
  the 
  alternat- 
  

  

  